A Parasitic Displacement Measurement System for Suspended Coil in Joule Balance

Abstract

Alignment is very important for Kibble balances and the joule balance at the measurement uncertainty region of several parts in 108. In the joule balance, if the suspended coil is in a misalignment state, parasitic displacements including the horizontal displacements along the ${x}$ - and ${y}$ -axes and the angular displacements around the ${x}$ -, ${y}$ -, and z-axes, will be produced and introduce alignment errors during the measurement of the joule balance. It is key for the joule balance to measure these parasitic displacements of the suspended coil during the alignment stages. So this paper describes the parasitic displacements measurement method based on our laser interferometer system. By studying and discussing the decoupling methods, we can calculate the five degrees of freedom parasitic displacements without complicating the structures of the suspended coil. In addition, several uncertainty sources have been theoretically analyzed to simplify the adjustment procedure during the parasitic displacements measurement. The experimental results show that the decoupling methods are effective for the parasitic displacements of the suspended coil, and this paper can contribute to a precise alignment in the joule balance.